To be able to add Cesc Fabregas to their midfield play is a tremendous luxury for Chelsea, and it helped stretch their Premier League lead to seven points in a game more stressful than England’s best team would have hoped for.

One measure of Chelsea’s strength is that Fabregas - and Willian - have been largely back-up players in Antonio Conte’s masterplan. Yet Fabregas, in this form, is capable of both hurtful passing and clever orchestration.

Conte is on a roll with his selections. His squad shuffling at Wembley on Saturday caused alarm, but was vindicated by a rousing 4-2 FA Cup semi-final win over Spurs, in which Chelsea’s manager used the bench to devastating effect. This time, Fabregas added a third midfield presence from the start, and grew in influence throughout he game until Pedro replaced him in the 76th minute. The hug and back-slap he received from Conte told a story.

Fabregas had brought his experience and composure to bear on a torrid phase of play for the league leaders in mid-game, and had seen them through to a 3-1 lead. He played a part in three of Chelsea goals and passed confidently, long and short. With his laying on of constructive balls, he allowed Diego Costa and Eden Hazard to maintain a level of threat even when neither was especially precise in the use of those opportunities.

Any thought that Chelsea’s entertaining FA Cup win would restore their finest league form was confounded by an anxious, messy performance against Southampton, who, given their location, know a thing or two about smooth sailing, and how to disrupt it.

Chelsea will probably win this Premier League title race, but their progress remains jerky. Before Gary Cahill sent Conte into fits with Chelsea’s second of the game, in first-half stoppage time, the prospective champions were overwhelmed by Southampton’s energy, and allowed too many of their own moves to break down, often around Costa.

The Chelsea weapon of interchanges between Fabregas, Costa and Hazard looked devastating when it worked, but inspired Southampton to counter-attack when it went wrong.

With 37 goals in 31 previous league outings, the Saints have not done much marching in. Oriol Romeu’s equaliser, though, after chaotic Chelsea defending from a corner, was a reward for constant enterprise. Cahill’s header, which added to Hazard’s sixth-minute softener, brought relief flooding out of Conte, who had not enjoyed seeing his side assailed.

Winning the PFA player of the year top spots was a lot easier than subduing Southampton. The order of merit was N’Golo Kante first, Hazard second. Even with these three points gathered, both will still need to be at their best to make sure Spurs are held off in second place.

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Fabregas is congratulated by his manager Antonio Conte

The start made by Hazard suggested he had a point to prove about the order of the voting. He began with a barrelling run past Oriol Romeu, then clipped a Costa pass from right to left past Fraser Forster in the Southampton net. From then on in the first-half, strangely, his game went downhill.

Seventeen minutes in, Costa set him up, but Hazard curled his shot wildly high, prompting an agonised “no-oooo” from Conte. Twice more before half-time he fluffed shots on goal. Racing into Southampton’s penalty box, he turned back inside and passed to no-one in particular. Kante meanwhile was his usual far-sighted self, seeing events before they happened, but his passing higher up the pitch was less assured, and he was booked for a badly mistimed tackle on James Ward-Prowse.

Chelsea lost one Premier League game in the six months from October to March, but two in April, prior to Southampton’s visit. The win over Spurs at Wembley, with its Nemanja Magic thunderbolt, left a psychological impression, but gave no guarantee of a return to invincibility where it matters most, in league action, especially as Southampton had 10 days to prepare. The Wembley win sent them into their 15th cup final of the Roman Abramovich era, but made no difference to the narrowed four point-lead over Tottenham, who are now forced to respond at Crystal Palace.

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Diego Costa was back scoring goals

At this late stage in a title race, the top team need their manager to make good decisions on selection, and they need fringe players to support those who are struggling. To call Fabregas ‘fringe’ still sounds wrong, but he has not been one of Conte’s chosen ones. But when he needed to, he brought all his class to the party.

From the bench, Fabregas saw Costa add a fourth. By then, even John Terry was having a feel of the grass. Chelsea could afford to go all the way through their playbook. Conte will remember the last four days as special ones. Days when he called everything correctly.